A power supply unit converts main AC voltage to one or more regulated DC voltages supplied to one or more loads, such as the internal components of a computer, server, or other electrical device. A digitally controlled switching mode power supply unit typically includes a primary side for power factor correction (PFC) and AC-to-DC voltage conversion, and a secondary side for DC-to-DC voltage conversion. The primary side is under control of a first digital signal controller (DSC) and the secondary side is under control of a separate second DSC or a digital control chip.
Adaptive control is a control method used by a controller which must adapt to a controlled system with parameters which vary, or are initially not optimized. Applying adaptive control to switching mode power supplies improves system performance. However, due to the non-linearity of the power train circuitry to be controlled, designing control parameters used in such an adaptive control is challenging.
One conventional approach for designing a loop controller for a switching mode power supply is to initially design control loop parameters based on a small signal model and Bodeplot. There is a separate small signal model for the primary side and the secondary side. Small signal modeling is a common analysis technique used to approximate the behavior of nonlinear devices with linear equations. In this manner, the power supply can be modeled using a mathematical model. Stability theory is then applied to design the digital controller in order to ensure that the switched mode power supply operates with sufficient phase margin and gain margin. In other words, the loop controller is designed to ensure that the power supply can operate at both steady state condition and transient state condition. The designed control loop parameters are finalized by trial and error, which is extremely time consuming, such as ranging from a couple of days to a few weeks. Additionally, the system performance is still subject to temperature and environment changes, which result in changes to the control loop parameters. As such, optimized performance can not be achieved as operating conditions change.
Another approach for designing the loop controller for a switching mode power supply is based on a system identification technique. The system identification technique adds functionality to the second DSC on the secondary side of the power supply. The second DSC is configured to determine system characteristics of the switching mode power supply under the current operating condition and to then adjust the control loop parameters according to the determined system characteristics. Parameters of the secondary-side small signal model are identified and then the parameters of the secondary-side loop controller are adjusted accordingly. To determine the system characteristics, such as the transfer function of the small signal model, white noise is injected into the power supply. The second DSC calculates the variance and covariance resulting from the injected noise to determine the system characteristics. Proper control loop parameters are calculated using the determined system characteristics, and these calculated control loop parameters replace the previous control loop parameters in the small signal model used by the second DSC. However, it is impractical to implement the system identification technique in a functioning power supply since injecting white noise can impact the stability of the system and even damage the power supply. Further, implementation of the system identification technique results in significant signal processing burden which requires a more powerful and expensive second DSC.